Pregnant rats made folic acid deficient during 72 hours of gestation have been shown to produce young exhibiting malformations of the hind and fore limbs. These defects are associated with an osteochondrodysplasia similar to human pathologic states. The teratogenic model therefore provides a uniquely advantageous system by which various phenomena associated with normal and abnormal calcification can be investigated. The objectives of this study are to examine on particular days of gestation in both normal and abnormal limbs the specific activity, substrate specificity, distribution and localization of enzymes which have particular significance in skeletal tissues. The resulting data will be used to describe and identify certain biochemical events and characteristics associated with normal limb development and the biochemical lesions associated with the abnormal development. The enzyme assays will be performed using fractions obtained by differential centrifugation of both homogenates and digestates of fetal limbs. Due to the recent findings implicating matrix vesicles as the site of initial calcification special efforts will be made to isolate these vesicles and examine certain enzyme characteristics attributed to them. A number of the enzymes will be investigated by electron microscopical techniques in order to correlate the biochemical data with certain morphologic events.